单项选择题
A.the plant should be prohibited to supplying air
B.the plant should work at intervals
C.the plant should be added disinfector in time
D.we should check strength of activated sludge, ivory-white color is best
单项选择题 Disinfector in the sewage biological treatment plant usually is （）
单项选择题 Before marine sewage treatment plant works （） should be filled with fresh water.
单项选择题 When does auxiliary burner of rotary nozzle incinerator begin to work? （） Ⅰ.hen igniting Ⅱ.he sludge for dealing with is too much Ⅲ.efore stopping incinerator